I went for a long walk (and long conversation) with a friend once and talking while chewing on dried peaches made me temporarily fluent. I think speaking clearly with our mouths full is a challenge in itself that's easier to succeed at. I assume that the effect will eventually wear off and one day you'll stutter despite chewing gum. But in the meantime it could also give you the opportunity to learn to work through your stutter just from the experience being fluent. Anyway, it might be frowned upon on its own, but if you're suddenly fluent during a presentation when everyone expects you to stutter I think you'll be totally excused for chewing gum.